text: /* LibTomCrypt, modular cryptographic library -- Tom St Denis
   *
   * LibTomCrypt is a library that provides various cryptographic
   * algorithms in a highly modular and flexible manner.
   *
   * The library is free for all purposes without any express
   * guarantee it works.
   *
   * Tom St Denis, tomstdenis@gmail.com, http://libtom.org
   */
  #include "tomcrypt.h"
  
  /**
    @file dsa_encrypt_key.c
    DSA Crypto, Tom St Denis
  */  
  
  #ifdef LTC_MDSA
  
  /**
    Encrypt a symmetric key with DSA
    @param in         The symmetric key you want to encrypt
    @param inlen      The length of the key to encrypt (octets)
    @param out        [out] The destination for the ciphertext
    @param outlen     [in/out] The max size and resulting size of the ciphertext
    @param prng       An active PRNG state
    @param wprng      The index of the PRNG you wish to use 
    @param hash       The index of the hash you want to use 
    @param key        The DSA key you want to encrypt to
    @return CRYPT_OK if successful
  */
  int dsa_encrypt_key(const unsigned char *in,   unsigned long inlen,
                            unsigned char *out,  unsigned long *outlen, 
                            prng_state *prng, int wprng, int hash, 
                            dsa_key *key)
  {
      unsigned char *expt, *skey;
      void          *g_pub, *g_priv;
      unsigned long  x, y;
      int            err;
  
      LTC_ARGCHK(in      != NULL);
      LTC_ARGCHK(out     != NULL);
      LTC_ARGCHK(outlen  != NULL);
      LTC_ARGCHK(key     != NULL);
  
      /* check that wprng/cipher/hash are not invalid */
      if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
         return err;
      }
  
      if ((err = hash_is_valid(hash)) != CRYPT_OK) {
         return err;
      }
  
      if (inlen > hash_descriptor[hash].hashsize) {
         return CRYPT_INVALID_HASH;
      }
  
      /* make a random key and export the public copy */
      if ((err = mp_init_multi(&g_pub, &g_priv, NULL)) != CRYPT_OK) {
         return err;
      }
     
      expt       = XMALLOC(mp_unsigned_bin_size(key->p) + 1);
      skey       = XMALLOC(MAXBLOCKSIZE);
      if (expt == NULL  || skey == NULL) {
         if (expt != NULL) {
            XFREE(expt);
         }
         if (skey != NULL) {
            XFREE(skey);
         }
         mp_clear_multi(g_pub, g_priv, NULL);
         return CRYPT_MEM;
      }
      
      /* make a random x, g^x pair */
      x = mp_unsigned_bin_size(key->q);
      if (prng_descriptor[wprng].read(expt, x, prng) != x) {
         err = CRYPT_ERROR_READPRNG;
         goto LBL_ERR;
      }
      
      /* load x */
      if ((err = mp_read_unsigned_bin(g_priv, expt, x)) != CRYPT_OK) {
         goto LBL_ERR;
      }
      
      /* compute y */
      if ((err = mp_exptmod(key->g, g_priv, key->p, g_pub)) != CRYPT_OK) {
         goto LBL_ERR;
      }
      
      /* make random key */
      x        = mp_unsigned_bin_size(key->p) + 1;
      if ((err = dsa_shared_secret(g_priv, key->y, key, expt, &x)) != CRYPT_OK) {
         goto LBL_ERR;
      }
  
      y = MAXBLOCKSIZE;
      if ((err = hash_memory(hash, expt, x, skey, &y)) != CRYPT_OK) {
         goto LBL_ERR;
      }
      
      /* Encrypt key */
      for (x = 0; x < inlen; x++) {
        skey[x] ^= in[x];
      }
  
      err = der_encode_sequence_multi(out, outlen,
                                      LTC_ASN1_OBJECT_IDENTIFIER,  hash_descriptor[hash].OIDlen,   hash_descriptor[hash].OID,
                                      LTC_ASN1_INTEGER,            1UL,                            g_pub,
                                      LTC_ASN1_OCTET_STRING,       inlen,                          skey,
                                      LTC_ASN1_EOL,                0UL,                            NULL);
  
  LBL_ERR:
  #ifdef LTC_CLEAN_STACK
      /* clean up */
      zeromem(expt,   mp_unsigned_bin_size(key->p) + 1);
      zeromem(skey,   MAXBLOCKSIZE);
  #endif
  
      XFREE(skey);
      XFREE(expt);
      
      mp_clear_multi(g_pub, g_priv, NULL);
      return err;
  }
  
  #endif
  /* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_encrypt_key.c,v $ */
  /* $Revision: 1.9 $ */
  /* $Date: 2007/05/12 14:32:35 $ */
  
  